Methods and systems for compressing and transmitting media signals are known in the art. Compressed digital video is largely becoming the preferred medium to transmit to video viewers everywhere. Parts of the Moving Pictures Experts Group (MPEG) specifications are standardized methods for compressing and transmitting video. Various audio compression techniques are also known in the art. In general, MPEG is used today for transmitting video over terrestrial, wireless, satellite and cable communication channels and also for storing digital video.
An audio stream is organized as an ordered sequence of frames. A video stream is usually organized as an ordered sequence of pictures; each picture includes a plurality of pixels. A video picture includes a plurality of slices, each slice including a plurality of macro blocks. The audio and video streams are provided to an audio encoder and to a video encoder respectively to generate compressed audio and video elementary streams, also referred to as elementary streams.
Elementary streams are packetized to produce PES packets. PES packets made up of elementary streams that form a program share a common time base. The PES packets may also include additional information. PES packets of distinct elementary streams can be arranged as either a Program Stream or a Transport Stream. At least one or more stream of PES packets having a common base time are usually combined to a Program Stream.
A Transport stream combines one or more programs with one or more independent time bases into a single stream. Transport streams include transport packets of 188 bytes. Transport stream packets start with a transport packet header. The header includes a packet ID (PID). Transport stream packets of one PID value carry data of a single elementary stream. Transport streams include Program Specific Information (PSI) tables. The PSI tables specify which PIDs and accordingly which elementary streams are associated to form each program.
Transport streams can include a single program of a multiplex of different programs. The latter is known as Multiple Program Transport Stream (MPTS).
Transport streams are designed to convey media (video and/or audio) signals. Other communication protocols can convey multiple information types that differ from video. These communication protocols are not tailored to carry only video and can carry video as well as other types of information. Such communication protocols are referred to as Multi Purpose Communication Protocols (MPCPs).
Usually, communication networks use a stack of communication protocols. The seven layer OSI model includes seven layers, while other commonly used protocol stacks include a different amount of layers.
MPCP protocols are usually the lower layer protocols of a protocol stack. They may include inter-network layer protocols, network interface layer protocols, and even transport layer communication protocols that differ from the MPEG transport stream.
Some commonly used MPCP protocols are ATM, IP, UDP, Ethernet, GigaEthernet, and the like.
One common protocol stack includes MPEG Transport stream, UDP, IP and Ethernet. Accordingly, an MPCP thread that conveys such an MPEG Transport stream includes MPEG Transport packets that are encapsulated within IP packets, UDP packets, Ethernet frames, and the like.
FIG. 1 illustrates a prior art Ethernet frame 90. Ethernet frame 90 includes an Ethernet header 91, an IP header 92, a UDP header 93, an Ethernet frame trailer 94 as well as multiple MPEG Transport packets 75. An exemplary transport packet (of a MPEG Transport) 75 includes transport stream payload (not shown) and a transport stream header. Various fields of the transport stream header are shown. Some are omitted for simplicity of explanation. The illustrated fields of the transport stream header include: a transport error indication bit 81, PID field 82, continuity counter field 83, discontinuity indicator field 85, and PCR field 87. The discontinuity indicator field 85 is a part of an adaptation field 84. The PCR field 87 is a part of optional fields 86.
A modern multiple purpose communication network includes multiple purpose components, such as routers, switches and the like. In order to improve the resilience of the multiple purpose communication network many components receive an MPCP thread and a duplicate MPCP thread.
Some of these multiple purpose communication network component are able to perform various MPCP operations. They are not capable of performing video related operations.
These MPCP operations may include processing MPCP information, performing error corrections based upon the MPCP information, requesting a re-transmission of certain MPCP packets, re-arrangement, assembling and fragmentation and the like.
For example, the MPCP processing may include retrieving or extracting an IP header, a UDP header and/or an Ethernet header or trailer, in order to detect IP layer failures, UDP layer failures, Ethernet layer failures and the like. These error can include Ethernet link loss, no IP relevant activity, no data on the relevant UDP port and the like.
Various well-known methods for providing redundancy are known in the art. U.S. Pat. No. 5,959,972 of Hamami, titled “method of port/link redundancy in an ATM switch”; U.S. Pat. No. 6,289,017 of Shami et al., titled “Method of providing redundancy and load sharing among multiple LECs in an asynchronous mode network”; U.S. Pat. No. 6,222,820 of Hamami, titled “method of VCC/VPC redundancy for asynchronous transfer mode networks”; U.S. patent application 20020076143 of Foltzer, titled “Multi-channel, multi-mode redundant optical loop having a bus topology”; U.S. patent application 20030110409 of Gale, et al. titled “method and apparatus for network fault correction via adaptive fault router”, all being incorporated herein by reference, provide a brief view of some state of the art redundant networks a method for providing redundancy.
Typically, once a link fails the traffic that was conveyed over the link is re-directed—routed through another link. If the link conveyed bi-directional traffic, the bi-directional traffic is re-routed.
U.S. Pat. No. 5,959,972 describes a method for implementing redundancy of both links and ports between two switches, e.g., ATM switches. A redundant link connection between two ATM switches is constructed using two separate parallel communication links connected between separate ports on each of the switches. One communication link is termed the main link and the other is termed the backup link. Two virtual circuits are setup between the backup link ports. One is a direct virtual circuit directed over the backup link. The other is an indirect virtual circuit that is routed over the main link via the main link ports. A virtual circuit is also setup over the main link for regular data traffic. In addition, a standby virtual circuit is setup over the backup link but is placed in standby until the occurrence of a failure. Until a failure occurs, traffic normally proceeds over the main link while the backup link ports transmit keep alive messages to each other over the indirect virtual circuit that is routed over the main link. When the main link fails, either one or both of the backup link ports detects the failure. The data traffic is then switched from the main link to the backup link. The failure is detected by the failure of the backup link ports to receive keep alive messages.
U.S. patent application 20020076143 describes an optical local loop having a bus topology with a pair of optical fibers disposed among a plurality of Optical Network Units (ONUs). A Host Digital Terminal (HDT) is disposed at the head end of the optical local loop for concentrating optical signals for a network. Redundant transceiver banks are provided within the HDT for operating with the optical signals effectuated at a plurality of wavelengths which are multiplexed and de-multiplexed via a pair of Wavelength Division Multiplex (WDM) connecters disposed on corresponding optical fibers. During transmission, the ONUs excite both optical fibers and the received optical signals are monitored in the HDT for quality and integrity of the optical paths. A selectively actuatable mechanism is provided in the HDT to switch downstream transmission to the ONU nodes from one optical path to the other optical path of the local loop based on the path quality and integrity.
Once a MPCP failure is detected the multiple purpose communication network component switches from one MPCP thread to the secondary MPCP thread. Thus, it switches from one MPTS to another MPTS, such as a duplicate MPTS.
The switching between a first MPTS to a second MPTS may can cause temporary visual artifacts or otherwise temporarily reduce the quality of multiple programs, including programs that were properly conveyed over the multiple purpose communication network.
In addition, in cases that both MPCP threads are partially damaged, the transition can result in a replacement of one or more programs by one or more defective duplicate programs.
There is a need to provide systems and method for providing redundancy in a more efficient manner.